Abstract: Graft polymers for use as compatibilizers and/or modifiers for engineering thermoplastic compositions are provided comprising the reaction product of functionalized thermoplastic polymers with styrene-maleic anhydride copolymer. The functionalized thermoplastic polymers are based typically on polyolefin polymers and contain at least one functional group reactive either with styrene-maleic anhydride copolymer, or with direactive linking groups reactive with both of the functionalized thermoplastic polymer and styrene-maleic anhydride copolymer. The engineering thermoplastic compositions to be modified include polar engineering thermoplastics and the non-polar engineering thermoplastics based on styrene.